FOOD-CROP-BASED PRODUCTION SYSTEMS AS SUSTAINABLE ALTERNATIVES FOR IMPERATA GRASSLANDS

Purely annual crop-based production systems have limited scope to be s ustainable under upland conditions prone to infestation by Imperata cy lindrica if animal or mechanical tillage is not available. Farmers who must rely on manual cultivation of grassland soils can achieve some s uccess in suppressing Imperata for a number of years using intensive r elay and intercropping systems that maintain a dense soil cover throug hout the year, especially where leguminous cover crops are included in the crop cycle. However, labour investment increases and returns to l abour tend to decrease in successive years as weed pressure intensifie s and soil quality declines. Continuous crop production has been susta ined in many Imperata-infested areas where farmers have access to anim al or tractor draft power. Imperata control is not a major problem in such situations. Draft power drastically reduces the labour requiremen ts in weed control. Sustained crop production is then dependent more s olely upon soil fertility management. Mixed farming systems that inclu de cattle may also benefit from manure application to the cropped area , and the use of non-cropped fallow areas for grazing. In extensive sy stems where Imperata infestation is tolerated, cassava or sugarcane ar e often the crops with the longest period of viable production as the land degrades. On sloping Imperata lands, conservation farming practic es are necessary to sustain annual cropping. Pruned tree hedgerows hav e often been recommended for these situations. On soils that are not s trongly acidic they may consistently improve yields. But labour is the scarcest resource on small farms and tree-pruning is usually too labo ur-intensive to be practical. Buffer strip systems that provide excell ent soil conservation but minimize labour have proven much more popula r with farmers. Prominent among these are natural vegetative strips, o r strips of introduced fodder grasses. The value of Imperata to restor e soil fertility is low, particularly compared with woody secondary gr owth or Compositae species such as Chromolaena odorata or Tithonia div ersifolia. Therefore, fallow-rotation systems where farmers can interv ene to shift the fallow vegetation toward such naturally-occurring spe cies, or can manage introduced cover crop species such as Mucuna utili s cv. cochinchinensis, enable substantial gains in yields and sustaina bility. Tree fallows are used successfully to achieve sustained croppi ng by some upland communities. A variation of this is rotational hedge row intercropping, where a period of cropping is followed by one or mo re years of tree growth to generate nutrient-rich biomass, rehabilitat e the soil, and suppress Imperata. These options, which suit farmers i n quite resource-poor situations, should receive more attention.